Analysis of electrical transients in the fourth quadrant of thin films photovoltaics: The case of organic bulk heterojunction solar cell

Author(s)

Pereira da Cunha, Mariana Richelle ^[1] ; Bezerra Amorim, Daniel Roger ^{[1, 2]} ; Faria, Gregorio Couto ^[1] ; Coutinho, Douglas Jose ^[3] ; Faria, Roberto Mendonca ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Fis Sao Carlos, POB 369, BR-13560970 Sao Carlos, SP - Brazil

^[2] Fed Inst Piaui Piaui IFPI, BR-64410000 Angical Do Piaui, PI - Brazil

^[3] Fed Univ Technol Parana UTFPR, BR-85902490 Toledo, PR - Brazil

• Document type: Journal article
• Source: SOLAR ENERGY MATERIALS AND SOLAR CELLS; v. 231, OCT 2021.
• Web of Science Citations: 0

Abstract

Current-voltage (J-V) measurements under illumination are essential for studying solar cells. They directly provide fundamental parameters of the solar cell, as the short-circuit current (J(SC)), the open-circuit voltage (V-OC), and the fill-factor (FF); but a deeper investigation of transport phenomena along the fourth quadrant is hampered by the tight linear scale, limited between zero to similar to 1 V. In this work, we present transient measurements carried out in an organic solar cell (ITO/PEDOT:PSS/PTB7-Th:PC71BM/Ca/Al), which allows to analyze J-V curves, by extending the scale from a linear to a logarithmic scale. For this, we used a circuit similar to that used in transient measurements, by replacing the voltage source by a variable load resistance R-L (from 50 Omega to 1 M Omega). A voltage transient Delta V(t) and its time decay tau are measured over each R-L, and tau-R-L curves were obtained, keeping the device under different intensities of sunlight. Each tau-R-L curve is divided in three distinct zones: one in which the extraction dominates the photocurrent; the second where a competition between extraction and non-geminate recombination is established; and the third, dominated by recombination and diffusion. An equivalent circuit is used to analyze the tau-R-L curves, in which the diode resistance plays a relevant role, especially in the region close to V-OC. Not only recombination mechanisms can be better analyzed through this new approach, but also the distinction between drift and diffusion transports. (AU)

• FAPESP's process: 14/50869-6 - INCT 2014: on Organic Electronics
• Grantee: Roberto Mendonça Faria
• Support Opportunities: Research Projects - Thematic Grants